Low-alloy steel castings crack can be divided into hot crack and cold crack. Due to the liquid steel is formed by shrinkage and deformation at high temperature. The stress is generated after low alloy steel casting cooling and shrinkage are blocked, when the stress exceeds the strength or plastic limit of the molten steel at the temperature,the crack will be generated.
Low alloy steel casting crack causes are as below:
(1) sulfur, phosphorus and other harmful elements are high enough to form a hot crack;
(2) steel inclusions and segregation easily lead to stress concentration;
(3) the line shrinkage of molten steel is more , the tendency of hot cracking is more;
(4) low alloy steel sand casting design structure is not easy to produce localized stress concentration, but also lead to thermal cracking;
(5) higher molten steel pouring temperature is more easy to produce hot cracks;
(6) low alloy steel casting gate cup and riser arrangement position isn’t improper and result in contraction blocked and hot cracks;
(7) sand and plastic pestle is too tight, poor concession, hinder contraction,it will increase the tendency of hot cracking;
(8) low alloy steel casting cooling rate is too fast or shakeout is earlier that all will make a greater premature cooling stress and increase the tendency of hot cracking;
(9) low alloy steel sand castings cut gate cup, improper riser or improper cleaning,the cooling is too fast or uneven after heat treatment will also lead to hot cracking;
(10) low-alloy steel sand castings cooled in lower temperature range, the cold crack is formed due to low alloy steel casting’s residual stress or external conditions .