AISI 4340 is one of the most widely used steels in high-risk industries such as military, nuclear and aerospace. The strength of this steel is capable of increasing to 1 825 MPa with quench and temper heat treatment, but it results in low toughness, low impact properties and brittle-fracture especially at low temperatures. In this study, the intermediate quenching treatment was used to induce ferritic–martensitic dual-phase (∼50/50 ferrite/martensite) microstructure that led to an impact energy of 93.6 kJ m−2, which was 241% higher than that of quench and temper treatment. Moreover, mechanical tests revealed tensile strength and hardness of 911.5 MPa and 43 HRC, respectively. Also, fractographic analysis confirmed the occurrence of the desirable ductile fracture mechanism.
Purpose
This study aims to investigate the effect of post heat treatment on mechanical properties of NiCrBSi coatings, which were applied on 316L stainless steel using high-velocity oxygen-fuel (HVOF) and flame spray techniques.
Design/methodology/approach
The properties of coatings were investigated by metallographic characterizations as well as wear, micro-hardness and adhesion tests.
Findings
The micro-hardness results showed that the coatings considerably increased the sub-layer hardness. In addition, regarding the wear test results, it can be seen that heat treatment increased wear resistance of the coatings. These thermal sprayed coatings are usually re-melted by post heat treatment, leading to improvement in tribological properties. The results obtained revealed that re-melting procedure improved the metallurgical bonding in the substrate\coating interface.
Originality/value
Microstructure defects resulting from thermal spraying such as pores and unmelted particles can be eliminated by post heat treatment. This process can considerably improve the corrosion and wear resistances of the thermal sprayed coatings.
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