1、1Chapter 3 Alloying of steelsSchool of Manufacturing Science and Engineeringv0. Introductionv1. Alloying elements in steelv2. Role of alloying elements on steelv3. Strengthening mechanisms of steelv4. Approach to improve the Plasticity and toughnessv5. Effects of alloying elements on phase transform
2、ation of steelv6. Metallurgical quality of steelContentsSchool of Manufacturing Science and Engineering30 IntroductionuAlloying：add the appropriate elements to change the propertiesu Why alloying？ucarbon steel：产量大、价格便宜、加工容易产量大、价格便宜、加工容易淬透性淬透性J、回火稳定性差、回火稳定性差uCast iron：石墨严重破坏铸铁基体力学性能石墨严重破坏铸铁基体力学性能Scho
3、ol of Manufacturing Science and Engineering40 IntroductionuMain elements ：Cr、Ni、Mo、W、V Existed elements：Mn、Si uNote: the alloying elements to affect the phase change process to improve the performancelow alloy steel： 5%medium alloy steel： 510%high alloy steel： 10%School of Manufacturing Science and
4、Engineering51. Alloying elements in steel1.1 Distribution of Alloying elements in steel：B、C、N；：Al、Si：Ti、V、Cr、Mn、Co、Ni、Cu、：Zr、Nb、Mo：W：稀土元素、：稀土元素、TaS、PImpurity elements School of Manufacturing Science and Engineering61. Alloying elements in steel1.1 Distribution of Alloying elements in steelExisting f
5、orm of Alloying elements *： Solution in the F, A, or Msolid solution（固溶体）（固溶体） The formation of the strengthening phase; (carbides or intermetallic compounds) - strengthening phase（强化相）（强化相） The formation of nonmetallic inclusions; (oxides, nitrides, or sulfides, etc.) - the second phase（第二相）（第二相） E
6、xist in the free state. simple substance（单质）（单质）Depending on the types, characteristics, content, smelting and heat treatment processSchool of Manufacturing Science and Engineering71. Alloying elements in steel1.2 Classification of alloying elements (1) Interaction between alloying elements and iron
7、vA（austenite）formed elements：C、N、Mn、Cu、Ni、Co，(Priority distribution on A)Austenitic ability =Ni%+30C%+30N%+0.5Mn%+0.25Cu% vF（ferrite）：）：Cr、V、Si、Al、Ti、Mo、W，(Priority distribution on F)School of Manufacturing Science and Engineering81. Alloying elements in steel1.2 Classification of alloying elements
8、(2) Interaction between alloying elements and carbonvNon-carbide forming elements ：Al、Si、Cu、Ni、P，(Solid solution or impurity)vCarbide forming elements ：Cr、V、Ti、Mo、 Zr、Nb，(Carbide or solid solution)School of Manufacturing Science and Engineering91. Alloying elements in steel1.2 Classification of allo
9、ying elements (3) Austenitic stacking fault energy（奥氏体层（奥氏体层错能）错能） 1）Improving：Cu、Ni、C； 2）Weakening： Mn、 Cr、Ru(钌钌)、Ir(铱铱) 。层错是一种晶体缺陷，它破坏了晶体排列的周期性，引起能量升高。产生单层错是一种晶体缺陷，它破坏了晶体排列的周期性，引起能量升高。产生单位面积的层错所需能量为位面积的层错所需能量为“层错能层错能” 。（。（层错能愈小，出现层错的几率层错能愈小，出现层错的几率愈大愈大）面心立方结构层错能低面心立方结构层错能低 School of Manufacturing
10、Science and Engineering102. The role of alloying elements on steel2.1 Interaction between alloying elements and iron2.2 Interaction between alloying elements and carbon2.3 Stacking fault energy of austeniteSchool of Manufacturing Science and Engineering112. The role of alloying elements on steel2.1
11、Interaction between alloying elements and ironPurpose：Using the interaction of the elements and iron, controlling the type and content of the alloy elements in the steel to obtain the desired microstructure1394Cg-g-FeFCCa-a-FeBCCd-d-FeB BCC912CSchool of Manufacturing Science and Engineering122. The
12、role of alloying elements on steel2.1 Interaction between alloying elements and iron（1）Expanding area： Mn、Ni、Co、 C、N、 Cu（A4、A3）Fe-M无限互溶无限互溶Fe-M有限互溶有限互溶School of Manufacturing Science and Engineering132. The role of alloying elements on steel2.1 Interaction between alloying elements and iron（2）reduci
13、ng area： Cr、V、Si、 Al、Ti、Mo、W（A3、A4）v 与与F无限互溶元素无限互溶元素:使奥氏体区被封闭；使奥氏体区被封闭； （ Cr、V、Si、Al、Ti、Mo、W）v 与与F有限互溶元素有限互溶元素:使使A区缩小。区缩小。 （ B、Nb、Ta、Zr）School of Manufacturing Science and Engineering142. The role of alloying elements on steel2.1 Interaction between alloying elements and ironInfluencing factors ： La
14、ttice type, the size and structure of the atoms, and electrochemical factors.合金元素与铁还可能形成金属间化合物合金元素与铁还可能形成金属间化合物 。 （如（如Fe-Cr、Fe-V、Fe-Mo等合金）等合金）总结：运用合金元素和铁的相互作用规律，控制合总结：运用合金元素和铁的相互作用规律，控制合金元素种类和含量，得到所需要的组织。金元素种类和含量，得到所需要的组织。School of Manufacturing Science and Engineering152. The role of alloying eleme
15、nts on steel2.1 Interaction between alloying elements and ironEngineering meanings： Using the interaction between alloy elements and iron， to require the needed structure. 特例：特例：OCr18Ni9TiSchool of Manufacturing Science and Engineering162. The role of alloying elements on steel2.2 Interaction betwee
16、n alloying elements and carbon表现在是否形成碳化物或形成碳化物倾向性的大小。表现在是否形成碳化物或形成碳化物倾向性的大小。（strengthening phase）Research purpose：l Types, character and distribution of carbide in the steel.l The influence on the phase transformation.School of Manufacturing Science and Engineering172. The role of alloying elements
17、on steel2.2 Interaction between alloying elements and carbon(1)non-carbide forming element(非碳化物形成元非碳化物形成元素素)：不与不与C形成化合物，但可固溶于形成化合物，但可固溶于a a-Fe或或g g-Fe中，中，或形成氮化物等化合物。或形成氮化物等化合物。 elements：Ni、Cu、Si、Co、Al、N、P等等School of Manufacturing Science and Engineering182. The role of alloying elements on steel2.2
18、Interaction between alloying elements and carbon (2)Carbide forming element(碳化物形成元素碳化物形成元素)： （Fe、Mn、Cr、W、Mo、V、Nb、Zr、Ti）a) 周期表中周期表中Fe的的“左左” ，但有例外！，但有例外！Ni, Co can form into cabon, but its stability is lower than Fe3C.Mn is easy to solid-soluted into Fe3C，forming alloy cementite.b) d电子层未满电子层未满：碳化物具有金属
19、键结合的性质：碳化物具有金属键结合的性质c) Stability of carbide：主要由：主要由d电子层电子层的未填满程度决定。的未填满程度决定。 由强到弱由强到弱：Ti, Zr, Nb, V, Mo, W, Cr, Mn, FeSchool of Manufacturing Science and Engineering192. The role of alloying elements on steel2.2 Interaction between alloying elements and carbonDifferent type of the carbide:(1) rc / r
20、me 0.59 : complex lattice carbide Cr23C6, Cr7C3, Fe3C (2) rc / rme 150）：）：slowing M decomposition is due to the strong carbide formation elements hindering C precipiting from M.5. Effects of alloying elements on phase transformationSchool of Manufacturing Science and Engineering815.4 Effect of alloy
21、 elements on tempering（1）Effect on M decomposition :（effect of carbon elements on it）In carbon steel, carbon precipitation temperaure is 250-350 ；In alloy steel, is 400-500 .carbon elements:V、Nb、Cr、Mo、W. non-carbide has little effect on this process, Si can slow M decomposition 。5. Effects of alloyi
22、ng elements on phase transformationSchool of Manufacturing Science and Engineering825.4 Effect of alloy elements on tempering（2）Effect on retained austenite tansformaionLittle retained austenite exist in the low carbon and low alloy steel after hardening, tempering temperature is 200-300，decompose i
23、t into M or B下下.The decomposition temperature of retained A rises when adding alloy elements, Cr、Mn、Si have the most remarkable effect.5. Effects of alloying elements on phase transformationSchool of Manufacturing Science and Engineering835.4 Effect of alloy elements on tempering（2）Effect on retaine
24、d A transformation In the high alloying elements containing a lot W、Mo、V、Cr，retained A preipitates carbon in the tempering process, Ms rising，exceeding room temperature, forming M after cooling.Hardness of hardening steel increases after tepering.5. Effects of alloying elements on phase transformati
25、on The phenomenon that retained A transform into M in tempering coolig in high alloying steel, hardness inceasing is called the secondary hardening（A-M）.School of Manufacturing Science and Engineering845.4 Effect of alloy elements on tempering（3）Effect on carbide formation, gathering together, growi
26、ng upv There is no influence of alloy elements on -carbon(Fe2.4C) forming.(got at low temperature tempering)v T回火回火， carbon transforms into cementite at 260 ; Si、Al、Cr will delay this transformation.（ Si、Al lead to the temperature rising to 350)v T回火回火，the diffusion of alloy elements：carbon forming
27、elements enrich in cementite, replacing Fe，formng alloying cementite and agglomeration. Si、V、W、Mo、Cr hinder it growing up.5. Effects of alloying elements on phase transformationSchool of Manufacturing Science and Engineering855.4 Effect of alloy elements on tempering（3）Effect on carbide formation, g
28、athering together, growing up在含在含W、Mo、V较多的钢中。较多的钢中。reasons：precipitating highly dispersed carbides from M in the tempering. stable at high temperature, not easy to gather and grow up.（Make it excellent high temperature strength）The secondary hardening5. Effects of alloying elements on phase transfor
29、mationSchool of Manufacturing Science and Engineering865.4 5.4 Effect of alloy elements on tempering（4 4）Effect on ferrite recrystallization回复（回复（reversion）：Structure has no obvious change, keep fibrous Structure has no obvious change, keep fibrous grain(grain(纤维状纤维状)；、H 、 、 change little；Residual s
30、tress significantly reduced.再结晶（再结晶（Recrystallization） ：The process of microstructure The process of microstructure reorganization.Grain shape changes, strength/hardness reorganization.Grain shape changes, strength/hardness significantly lower , plasticity/tenacity increased significantly lower , pl
31、asticity/tenacity increased significantly.significantly.5. Effects of alloying elements on phase transformationSchool of Manufacturing Science and Engineering875.4 Effect of alloy elements on tempering（4）Effect on ferrite recrystallizationMost alloy elements delay ferrite recrystallizationCo、Mo、W、V、
32、Cr improve recrystallization temperature，Ni influence little.eg.：In carbon steel，phase starts reversion process exceeding 400, recrystallization at 500；when adding 2%Co, recrystallization temperature can rise to630.5. Effects of alloying elements on phase transformationSchool of Manufacturing Scienc
33、e and Engineering885.4 Effect of alloy elements on tempering（5） The effect on temper brittleness Means the hardened steel after tempering happened to toughness decline phenomenon.v The first class temper brittleness ：low temperature temper brittleness, dont eliminate. generating temperature 450650。v
34、 reasons：retained austenite transformation；Carbide precipitation;Impurities partial polyv 加入加入Mo、W、V、Al can weaken little；Mn、Cr can promote；Si、Cr make it moving to higher temperatures.。5. Effects of alloying elements on phase transformationSchool of Manufacturing Science and Engineering895.4 Effect
35、of alloy elements on tempering（5） The effect on temper brittleness second class temper brittleness ： high temperature temper brittleness。generating temperature 450650。Mo、W can weaken；Mn、Cr、Ni can promote；v 防止：防止：rapid cooling after tempering（Avoid elements tsegregation at grain boundaries and precip
36、itatio.）Adding Mo、W inhibitting the second tempering brittlenessImprove the metallurgical quality, reduce the impurity elements in steel5. Effects of alloying elements on phase transformationSchool of Manufacturing Science and Engineering906. Metallurgical quality of steel钢材在生产过程中经过冶炼、铸造、轧制或锻造等工序，最后
37、成材。钢材在生产过程中经过冶炼、铸造、轧制或锻造等工序，最后成材。由这些过程所控制的质量，称为冶金质量。由这些过程所控制的质量，称为冶金质量。6.1 The macroscopic defects of steel： shrinkage porosity疏松疏松, shrinkage cavities缩孔缩孔, segregation偏析偏析,bubble气泡气泡,crack裂纹裂纹,flakes白点白点shrinkage porosity：组织不致密。措施：控制冶炼和铸锭质量，组织不致密。措施：控制冶炼和铸锭质量，减减少钢中气体和杂质。少钢中气体和杂质。segregation：化学成分不均匀
38、。化学成分不均匀。采用高温扩散退火。采用高温扩散退火。shrinkage cavities：凝固过程，体积收缩，在冒口一端出现。采取凝固过程，体积收缩，在冒口一端出现。采取正确浇注工艺、合理定型设计，并适当切除冒口。正确浇注工艺、合理定型设计，并适当切除冒口。School of Manufacturing Science and Engineering916. Metallurgical quality of steel6.2 high magnification defect of steel： Banded structure带状组织带状组织, non-metallic inclusion
39、s 非金属夹杂非金属夹杂,carbide liquid chromatography碳化物液碳化物液析析, widmanstatten structure魏氏组织魏氏组织, net carbide网状碳化物网状碳化物6.3断口分析：断口分析：（自学）（自学）School of Manufacturing Science and Engineering92补充内容合金元素对钢性能特点影响总结硅、锰、铬、镍、钼、钨、钒，钛，铌、硼、铝 v Cr 1、在低合金范围内，对钢具有很大的强化作用，提高强度、硬度和耐磨性 2、降低钢的临界冷却速度，提高钢的淬透性 3、提高钢的耐热性 4、使钢具有良好的抗腐蚀
40、性和抗氧化性 v Ni 1、 提高钢的强度，而不降低其韧性（低温韧性） 2、 降低钢的临界冷却速度，提高钢的淬透性 3、 扩大奥氏体区，是奥氏体化的有效元素 4、提高钢的抗腐蚀能力，不仅能耐酸，而且能抗碱和大气的腐蚀。School of Manufacturing Science and Engineering93v Mn 1、在低含量范围内，对钢具有很大的强化作用，提高强度、硬度和耐磨性 2、降低钢的临界冷却速度，提高钢的淬透性 3、稍稍改善钢的低温韧性 4、在高含量范围内，作为主要的奥氏体化元素v Al 1、 炼钢中起良好的脱氧作用 2、 细化钢的晶粒，提高钢的强度 3、提高钢的抗氧化性能
41、School of Manufacturing Science and Engineering94v Si 1、强化铁素体，提高钢的强度和硬度 2、降低钢的临界冷却速度，提高钢的淬透性 3、提高钢的氧化性腐蚀介质中的耐蚀性，提高钢的耐热性v RE 1、炼钢中起脱硫、去气、净化钢液作用 2、细化钢的晶粒，改善铸态组织 School of Manufacturing Science and Engineering95v钛(Ti)：钛是钢中强脱氧剂。 细化晶粒 改善焊接过程凝固脆性 在18-8奥氏体不锈钢中加入适当的钛，避免晶间腐蚀。 v钒(V)：钒是钢的优良脱氧剂。 钢中加0.5%的钒可细化晶粒，
42、提高强度和韧性。 钒与碳形成的碳化物。 School of Manufacturing Science and Engineering96v钨(W)：(1) 提高强度（2）提高钢的高温强度。（3）提高钢的抗氢性能。（4）是使钢具有热硬性。因此钨是高速工具钢中的主要合金元素。v铌(Nb)： 细化晶粒 降低钢的过热敏感性及回火脆性，提高强度，但塑性和韧性有所下降。 改善焊接性能。在奥氏体不锈钢中加铌，可防止晶间腐蚀现象。 School of Manufacturing Science and Engineering97Summarykey points：v The interaction between alloy elements and Fe, C. The effect of alloy elements on stacking fault energy.v Strengthening mechanism of steelv A basic way to improve the plasticity and toughness of steeldifficult points ：v The influence of alloy elements on the steel phase transition
