①細晶粒斷口、低塑性，多發(fā)生于冷加工后的Q345B方管。原因在結(jié)晶退火或正火時，加熱溫度偏低或保溫時間短，致使冷加工么過程中的破碎晶粒未能全部再結(jié)晶造成的。補救措施為：進行?f 晶退火，或進行一次完全退火或正火處理。

(1) Fine grain fracture and low plasticity occur mostly in Q345B square tube after cold working. The reason is that during crystallization annealing or normalizing, the heating temperature is low or the holding time is short, which results in the failure of recrystallization of the broken grains in the process of cold working. The remedial measures are as follows: annealing f crystal, or a complete annealing or normalizing treatment.

②硬度過髙對中碳鋼而言，多為退火時加熱溫度過高，冷巧度太快，或等溫溫度過低等;另外錯誤采用了正火處理;對于Q345B方管進行球化退火時，欠熱或過熱均會造成退火后硬度高的缺?爸或者因冷卻速度過快，等溫溫度過低或時間不足等。補救措 施：重新進行正火處理，如果組織合格，僅硬度高，則可進行一次 高溫回火處理。

(2) For medium carbon steel, excessive hardness is mainly due to excessive heating temperature, too fast cooling, or too low isothermal temperature during annealing; in addition, incorrect normalizing treatment is used; for Q345B square tube, underheating or overheating will cause high hardness after annealing, Dad or due to excessive cooling speed, too low isothermal temperature or insufficient time, etc. Remedial measures: Renormalizing treatment, if the organization is qualified, only high hardness, you can carry out a high temperature tempering treatment.

③出現(xiàn)網(wǎng)狀組織在共析鋼中先共析鐵素體或過共析鋼中的共析滲碳體沿晶界呈網(wǎng)狀分布，明顯降低了Q345B方管材料的力學(xué)性能，原因?在于退火溫度過高，或冷卻速度過慢所造成的。補救措施：再進行 一次正火處理，對過共析鋼正火后，應(yīng)再進行一次高溫回火，以改 善切削加工性能。

(3) The occurrence of reticulated structure in eutectoid steels with pre-eutectoid ferrite or eutectoid cementite in hypereutectoid steels shows a reticulated distribution along grain boundaries, which significantly reduces the mechanical properties of Q345B square tube material due to the excessive annealing temperature or slow cooling rate. Remedy: After normalizing the hypereutectoid steel, a high temperature tempering should be carried out again to improve the cutting performance.

④粗晶粒斷口一是退火或正火加熱溫度太髙，加熱時間長; 或經(jīng)過5%?15%的變形冷加工的再結(jié)晶時間過長，造成晶粒的異?常粗大，出現(xiàn)粗晶粒斷口，直接造成的力學(xué)性能和沖擊韌性的降低。 補救措施：對亞共析鋼采用正火或完全退火;對于過共析Q345B方管采用正?火+球化退火，或正火+髙溫回火，對于晶粒度1?2號的Q345B方管材料必須 采用兩次正火處理，第一次應(yīng)高出正常溫度50?150℃，但升溫速度?要快，時間應(yīng)盡可能的縮短，第二次則采用正常的正火溫度。

(4) The first is that the annealing or normalizing heating temperature is too high and the heating time is too long; or the recrystallization time after 5%? 15% deformation and cold processing is too long, which results in the abnormal grain size and the appearance of coarse grain fracture, which directly reduces the mechanical properties and impact toughness. Remedial measures: normalizing or complete annealing for hypoeutectoid steel; normalizing + spheroidizing annealing or normalizing + tempering for hypereutectoid Q345B square pipe; twice normalizing for Q345B square pipe material with grain size 1?2, the first should be higher than normal temperature 50?150 C, but the heating rate should be faster, the time should be shortened as far as possible, and the second should be normal normalizing temperature. Degree.

⑤出現(xiàn)石墨碳出現(xiàn)于高碳和含硅、鋁的鋼中，原因為加熱 溫度過高，保溫時間過長，使?jié)B碳體分解而析出石墨，嚴重的將降?低材料的強度，脆性增大，是無法挽救的。

Graphite carbon appears in high carbon and steel containing silicon and aluminium. The reason is that the heating temperature is too high and the holding time is too long, which causes the cementite to decompose and precipitate graphite. Seriously, it will reduce the strength of the material and increase its brittleness, which is irreversible.