本文關(guān)鍵詞：噴射成形新型熱作模具鋼的組織與性能研究　出處：《北京科技大學(xué)》2015年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 噴射成形 熱作模具鋼 高溫強(qiáng)度 組織 性能

【摘要】：H13鋼是世界范圍內(nèi)仍廣泛使用的熱作模具鋼,但等向性差和600℃以上熱強(qiáng)度不足等問題一直影響其使用壽命和應(yīng)用范圍。等向性差是由傳統(tǒng)鑄造的低冷速所引起的粗大一次碳化物與合金元素偏析造成的,而熱強(qiáng)度不足則主要與合金成分及碳化物種類、數(shù)量、分布有關(guān)。H13鋼含有較多的Cr(-5.0wt%),回火時(shí)主要析出熱穩(wěn)定性較低的M7C3型碳化物,該碳化物在600℃以上高溫回火時(shí)容易聚集長大,從而對(duì)高溫性能不利。鑒于此,本文采用噴射成形工藝來制備新型熱作模具鋼,利用其均勻細(xì)小的組織優(yōu)勢來改善傳統(tǒng)鑄造H13鋼的等向性,并通過調(diào)整合金成分來解決高溫強(qiáng)度不足的問題,同時(shí)研究了噴射成形工藝與合金元素對(duì)合金組織性能的作用規(guī)律,主要得出以下結(jié)論： 對(duì)H13鋼的合金成分進(jìn)行了改進(jìn),并利用噴射成形技術(shù)制備出了一系列高熱強(qiáng)性兼具韌性的噴射成形新型熱作模具鋼。在沖擊韌性與H13鋼相當(dāng)?shù)那闆r下,噴射成形新型熱作模具鋼的回火抗性、高溫強(qiáng)度、熱穩(wěn)定性、高溫磨損抗性、熱疲勞抗性都明顯高于H13鋼。尤其是高溫強(qiáng)度和熱穩(wěn)定性,其中700℃下的高溫抗拉強(qiáng)度平均提高了200MPa左右；而在660℃保溫12小時(shí)后的硬度更是由H13鋼的26.5HRC提高到了33HRC以上。噴射成形新型熱作模具鋼中最具代表性的合金成分為：Fe-0.37C-0.8Si-0.3Mn-3.0Cr-2.4Mo-1.5V-0.04Nb(wt%),該合金具有最好的高溫強(qiáng)度和高溫磨損抗性,700℃下高溫抗拉強(qiáng)度達(dá)到530MPa,比H13鋼提高了240MPa,400℃下的高溫磨損體積降低到H13鋼的1/7左右。 確定了適合新型熱作模具鋼和H13鋼的最佳噴射成形工藝參數(shù)：澆注溫度1600℃～1625℃,霧化壓力0.45MPa-0.50MPa。在此工藝下,噴射成形新型熱作模具鋼與H13鋼的沉積態(tài)組織為均勻細(xì)小的等軸晶組織,而非鑄態(tài)H13鋼中的粗大枝晶組織,并且晶粒細(xì)化到20-30μm,消除了粗大一次碳化物,明顯改善了碳化物與合金元素偏析,從而有助于提高等向性。探索出了適合噴射成形新型熱作模具鋼的最佳熱處理工藝：淬火溫度1040℃-1070℃,回火溫度620℃-640℃,保證其具有優(yōu)異的綜合性能。 研究發(fā)現(xiàn)噴射成形新型熱作模具鋼的高溫強(qiáng)度比H13鋼明顯提高的原因主要與回火組織中馬氏體的回復(fù)程度及碳化物的強(qiáng)化效果有關(guān)。H13鋼在650℃回火時(shí),馬氏體已回復(fù)完全,基體強(qiáng)度明顯下降,并在原馬氏體板條界和晶界上析出了較多的120nm左右的Cr7C3和M6C型碳化物,第二相強(qiáng)化效果降低；而噴射成型新型熱作模具鋼經(jīng)650℃回火后,基體依然為板條馬氏體,板條內(nèi)較高的位錯(cuò)密度確保了基體較高的強(qiáng)度,同時(shí)板條內(nèi)析出的大量細(xì)小彌散的薄片狀VC(片長～25nm,片厚～2.5nm)在起到彌散強(qiáng)化作用的同時(shí)還釘扎位錯(cuò),推遲了馬氏體的回復(fù),進(jìn)一步提高了組織穩(wěn)定性。 在合金元素作用規(guī)律方面,發(fā)現(xiàn)將H13鋼中的Cr含量降到3.0wt%,可明顯抑制回火時(shí)Cr7C3的析出,促進(jìn)VC析出,從而明顯提高回火抗性和700℃的高溫強(qiáng)度。增加Mo含量可進(jìn)一步抑制Cr7C3的析出,促進(jìn)VC析出并增加其穩(wěn)定性,進(jìn)一步增加700℃的高溫強(qiáng)度。W和Mo的作用基本類似,雖然W提高700℃高溫強(qiáng)度的能力不如Mo,但其提高熱穩(wěn)定性的能力高于Mo,其中添加0.6wt%W的7號(hào)合金在660℃保溫12h后的硬度最高,仍然保持在37HRC。這是因?yàn)樘砑拥腤可進(jìn)到回火二次析出的碳化物中,由于W遠(yuǎn)低于Mo的擴(kuò)散速率明顯降低了碳化物在高溫回火時(shí)的粗化速度,從而提高了熱穩(wěn)定性。 增加V含量可促進(jìn)VC析出并增加其穩(wěn)定性,同時(shí)抑制Cr7C3和M6C析出,從而提高700℃的高溫強(qiáng)度并抑制淬火時(shí)的晶粒長大。V和Mo復(fù)合增加不僅抑制Cr7C3的形成,促進(jìn)VC析出并增加其穩(wěn)定性,提高700℃的高溫強(qiáng)度,而且還增加了淬火時(shí)未溶碳化物的含量,從而提高高溫磨損抗性,但韌性有所降低。添加0.04wt%Nb就可抑制淬火時(shí)的晶粒長大,但當(dāng)Nb含量增加到0.12wt%時(shí)會(huì)導(dǎo)致合金沉積態(tài)組織中出現(xiàn)粗大一次VC和NbC,加劇合金元素偏析,從而對(duì)強(qiáng)韌性不利。 綜上所述,本論文利用噴射成形技術(shù)成功制備出高熱強(qiáng)性兼具韌性的新型熱作模具鋼,明顯改善了碳化物與合金元素的偏析并且極大的提高了高溫強(qiáng)度,為開發(fā)高性能熱作模具鋼提供了一條新的途徑。同時(shí)對(duì)合金元素Cr、Mo、W、V、Nb作用規(guī)律的認(rèn)識(shí)也可為高性能熱作模具鋼的合金設(shè)計(jì)提供一定的理論參考。
[Abstract]:H13 steel is widely used in the world are still hot die steel, but other issues to the poor 600 degrees above and lack of hot strength has to affect its service life and application range. To the poor is caused by conventional casting and low cooling rate of coarse primary carbides and segregation of alloy elements caused. The lack of hot strength of species composition and quantity distribution of carbide alloy,.H13 steel containing more Cr (-5.0wt%), M7C3 carbides during tempering stability of the main precipitation in the low heat, the carbide in high temperature above 600 DEG tempering easily gathered long, and on the high temperature performance disadvantage. In view of this, this paper the spray forming process to produce new hot working die steel, with its fine structure to improve the traditional advantages of H13 cast steel to high temperature, and to solve the problem of insufficient strength by adjusting the composition of the alloy were also studied. The effect of spray forming technology and alloying elements on the microstructure and properties of the alloy is mainly drawn as follows:
The alloy composition of H13 steel was improved, and the use of spray forming technology to prepare a series of thermal strength with toughness of spray forming new hot working die steel. The impact toughness of H13 steel and equivalent, spray tempering resistance, forming a new hot working die steel high temperature strength, thermal stability, high temperature the wear resistance and thermal fatigue resistance were significantly higher than that of H13 steel. Especially high temperature strength and thermal stability, the high temperature tensile strength at 700 DEG C increased by about 200MPa; while in the 660 DEG C for 12 hours after the hardness is made of H13 steel 26.5HRC increased to more than 33HRC. Spray forming alloy thermal model composition of die steel in the most representative is: Fe-0.37C-0.8Si-0.3Mn-3.0Cr-2.4Mo-1.5V-0.04Nb (wt%), the alloy has the best high temperature strength and high temperature wear resistance, high tensile strength under 700 DEG C to 530MPa, than H13 steel increased At 240MPa, the high temperature wear volume at 400 C is reduced to about 1/7 of H13 steel.
The optimum spray forming process parameters for the new hot die steel and H13 steel pouring temperature 1600 to 1625 DEG C, atomization pressure of 0.45MPa-0.50MPa. in this process, the microstructure of spray deposition forming new hot working die steel and H13 steel for the uniform and fine equiaxed crystals, rather than casting coarse dendrite microstructure in H13 steel, and the grain refinement to 20-30 m, eliminating the coarse primary carbides, carbides and improve the segregation of alloy elements, which is helpful to improve the other. To explore optimal thermal spray forming model for hot die steel process. The quenching temperature is 1040 DEG -1070 DEG, tempering the temperature of 620 DEG -640 DEG, which has excellent comprehensive performance.
The study found that recovery degree and the carbide causes high strength die steel thermal spray forming was better than the H13 steel and the main body in the tempering on strengthening effect of.H13 steel in 650 DEG C during tempering of martensite has been restored completely, the matrix strength decreased significantly, and the original martensite lath boundaries and grain boundaries. The precipitation of Cr7C3 and M6C carbides more about 120nm, second phase strengthening effect is reduced; and the injection molding new hot working die steel after tempering at 650 C, the matrix is lath martensite lath in high dislocation density matrix to ensure high strength, at the same time a large number of dispersed precipitation of thin slab VC (a ~ 25nm, ~ 2.5nm in thickness) to strengthen the role of diffusion and dislocation pinning, delayed martensite recovery, further improve the stability of structure.
The effect of alloy elements, it is found that Cr content in H13 steel can be reduced to 3.0wt%, the precipitation of Cr7C3 obviously inhibited the tempering, promote the precipitation of VC, can significantly improve the strength at high temperature tempering resistance and 700 DEG C. Precipitation increased the content of Mo can further inhibit Cr7C3, promote VC analysis and further increase the stability. The increase of high temperature of 700 DEG C strength.W and the role of Mo is similar, although the W improve high temperature strength of 700 DEG C ability than Mo, but its ability to improve the thermal stability of Mo is higher than that of 0.6wt%W, the hardness of alloy 7 at 660 DEG C for 12h after the high, remains at 37HRC. this is because the added W can enter into the two times tempering precipitated carbides, because W is far lower than the diffusion rate of Mo significantly decreased the coarsening of carbides during tempering at high speed, so as to improve the thermal stability.
The increase of V content can promote the precipitation of VC and increase its stability, and inhibition of Cr7C3 and M6C precipitation, the formation of grain so as to improve the high temperature strength of 700 DEG C and inhibit the quenching growth of.V and Mo composite increase not only inhibit Cr7C3 and promote the precipitation of VC and increase its stability, improve the strength at high temperature of 700 DEG C, but also increased the content of when quenching undissolved carbide, so as to improve the high temperature wear resistance, but the toughness decreased. Adding 0.04wt%Nb can inhibit the grain growth during quenching, but when the content of Nb increased to 0.12wt% will be a rough VC and NbC resulted in the microstructure of alloy deposition, thus increasing the segregation of alloying elements on the strength and toughness of disadvantage.
In summary, spray forming technology successfully prepared a new heat thermal strength with toughness of die steel in this paper, significantly improve the segregation of carbide and alloy elements and greatly improves the high temperature strength, provides a new way for the development of high performance hot die steel. At the same time, alloy elements Cr, Mo W, V, Nb, understanding the effect of can also provide a theoretical reference for the high performance of hot work die steel alloy design.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG142.1

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本文編號(hào)：1428099