回火熱處理對AR400H和AR500H耐磨鋼氫脆性質影響之研究

Abstract

AR400H和AR500H為低合金高強度鋼種，在工業上常應用於挖土機的鏟刀、自卸車的車斗、礦場的粉碎機刀刃等。在DQ熱處理後AR400H最大抗強度達1436MPa；AR500H最大抗拉強度達1837MPa，為麻田散鐵組織，屬於高強度合金鋼，然而高強度麻田散鐵容易受到氫脆影響，發生不可預期的破壞，故本實驗利用電化學方式對AR400H和A500H進行充氫，評估不同熱處理狀態下機械性質的變化，並配合顯微組織的觀察、熱脫氫分析量測，瞭解不同熱處理狀態下AR400H和AR500H氫脆差異的原因。 經由實驗發現AR400H在DQ和200o回火態氫捕集位置主要為差排；300o和400oC回火態氫捕集位置為雪明碳鐵和差排；AR500H在DQ態氫捕集位置主要為差排和殘留沃斯田鐵；300o和400oC回火態氫捕集位置為雪明碳鐵和差排。 AR500HDQ態具有最高氫含量1.03ppm且最差的抗氫脆能力；200o回火態和300o回火態拉伸曲線已達降伏強度抗氫脆能力提升；400oC回火態因強度下降及含氫量減少，抗氫脆能力再提升延伸損失率達50%；AR400H各回火狀態含氫量皆低於0.6ppm，且降伏強度皆低於1400MPa，因而在各熱處理狀態下，皆擁有極佳的抗氫脆能力延伸損失率皆小於20%。

AR400H and AR500H are low-alloy high-strength steel grades, which are commonly used in the industry for shovel blades of excavators, buckets of dump trucks, blades of crushers in mines, etc. After the DQ heat treatment, the UTS of AR400H reaches 1436MPa; the UTS of AR500H reaches 1837MPa, which belongs to high-strength alloy steel. However, the high-strength martensite is susceptible to hydrogen embrittlement and unexpected damage occurs. In this experiment, AR400H and A500H were electrochemically charged with hydrogen to evaluate the changes in mechanical properties under different heat treatment conditions, and combined with the observation of microstructure and thermal desorption analysis measurement to understand the difference between AR400H and AR500H hydrogen embrittlement under different heat treatment conditions. It is found through experiments that the hydrogen trapping size of AR400H in DQ and 200oC tempering state is mainly dislocation; the hydrogen trapping size of 300oC and 400oC tempering state is cementite and dislocation; the hydrogen trapping size of AR500H in DQ state is mainly dislocation and retained austenite; 300oC and 400°C tempering state, the hydrogen trapping size is cementite and dislocation. The AR500HDQ state has the highest hydrogen content of 1.03ppm and the worst hydrogen embrittlement resistance; the tensile curves of 200oC tempered state and 300oC tempered state have reached the yield strength and improved hydrogen embrittlement ability; the 400oC tempered state due to the decrease in strength and hydrogen content improved hydrogen embrittlement ability and elongation loss is reduced to 50%; AR400H has a hydrogen content of less than 0.6ppm and lower yield strength in each tempered state, so in each heat treatment state, it has excellent hydrogen embrittlement resistance and the elongation loss is less than 20 %.